Exceptions

  • Don’t use exceptions for flow of control.
    [link]

    1.   # bad
    2.   begin
    3.     n / d
    4.   rescue ZeroDivisionError
    5.     puts "Cannot divide by 0!"
    6.   end
    8.   # good
    9.   if d.zero?
    10.     puts "Cannot divide by 0!"
    11.   else
    12.     n / d
    13.   end

  • Avoid rescuing the Exception class.
    [link]

    1.   # bad
    2.   begin
    3.     # an exception occurs here
    4.   rescue Exception
    5.     # exception handling
    6.   end
    8.   # good
    9.   begin
    10.     # an exception occurs here
    11.   rescue StandardError
    12.     # exception handling
    13.   end
    15.   # acceptable
    16.   begin
    17.     # an exception occurs here
    18.   rescue
    19.     # exception handling
    20.   end

  • Don’t specify RuntimeError explicitly in
    the two argument version of raise. Prefer error sub-classes for clarity and
    explicit error creation.[link]

    1.   # bad
    2.   raise RuntimeError, 'message'
    4.   # better - RuntimeError is implicit here
    5.   raise 'message'
    7.   # best
    8.   class MyExplicitError < RuntimeError; end
    9.   raise MyExplicitError


  • Prefer supplying an exception class and a message as two separate arguments
    to raise, instead of an exception instance.
    [link]

    1.   # bad
    2.   raise SomeException.new('message')
    3.   # Note that there is no way to do `raise SomeException.new('message'), backtrace`.
    5.   # good
    6.   raise SomeException, 'message'
    7.   # Consistent with `raise SomeException, 'message', backtrace`.

  • Avoid using rescue in its modifier form.
    [link]

    1.   # bad
    2.   read_file rescue handle_error($!)
    4.   # good
    5.   begin
    6.     read_file
    7.   rescue Errno:ENOENT => ex
    8.     handle_error(ex)
    9.   end